The present invention relates to illumination and image processing and specifically to illumination with a narrow bandwidth illuminator to capture and produce color images.
In many applications of CMOS visible-light image capture and processing, so-called “white light”—meaning light exhibiting roughly equal intensities of many colors or wavelengths of in the visible light bandwidth—is used for illumination. One of the reasons white light has traditionally been used is because daytime image capture, especially outdoors, can easily take advantage of available direct or reflected sunlight (i.e. “daylight”) which is generally regarded as white light. Because image capture devices have traditionally been developed with sensitivities to sunlight, artificial illumination sources having white light characteristics have been widely applied where daylight/sunlight illumination is not available. Some white light illumination sources take advantage of mixing colored illuminations, as known in the art.
When systems or devices that capture color images capture are constrained to very low power requirements, white light illuminators, whether comprising a singular source or a combination of different colored illuminators, are not acceptable because they tend to exhibit higher energy consumption (due to, but not limited to: dissipated heat of a singular source; and additional power consumption of a combination of colored illuminators) in comparison to similar illuminators having a single color, having a narrow bandwidth, which typically exhibit lower power consumption.
In the specification and claims which follow hereinbelow, the term “narrow bandwidth” is meant to relate to an illuminator exhibiting peak intensity at a corresponding peak wavelength or wavelength range (i.e. “bandwidth”). The illuminator typically exhibits a spectral intensity function with lower illumination intensities for wavelengths other than the intensity corresponding to the peak wavelength or wavelength range. As such, the term “narrow bandwidth” is used to distinguish the peak intensity bandwidth from the entire spectral intensity function of the illuminator. Exemplary typical illuminators having a narrow bandwidth characteristic are red, blue, and green LEDs (light-emitting diodes). Narrow bandwidth illuminators, as referred to in the specification and claims hereinbelow, typically exhibit light in wavelengths substantially in the visible spectrum. A typical narrow bandwidth illuminator also exhibits light in wavelengths covering most of the visible spectrum, but with lower intensities than the peak intensity color (i.e. wavelength), where the characteristic wavelength(s) exhibit the strongest intensities.
Conventional image capture devices designed to capture white light have not heretofore been able to take advantage of a single color or narrow bandwidth illuminator to produce a full color image. Efforts in other fields of endeavor have been made to process incident light from such illuminators to enhance color images. Examples of such prior art are: US Patent Application publication no. 20020196337, by Tayekama, US Patent Application publication no. 20080158258, by Lazarus et al., and U.S. Pat. No. 6,839,522, by Grubb et al., all of whose disclosure are incorporated herein by reference.
There is therefore a need for a low power consumption, a low cost system and a method to take advantage of a narrow bandwidth illuminator to capture and produce color images.